1. Field of the Invention
The present invention relates generally to a gas generating device and more specifically to a gas generating device which mixes water with the hot gaseous combustion products of a solid propellant.
2. Description of the Related Art
Various gas generating arrangements have been proposed for the purposes of inflating a safety restraint device such as an air bag. However, many of these arrangements have simply released the hot combustion products into the inflatable device with very little modification other than screening to remove particulate matter.
In order to modify the gaseous products which are generated by the combustion of a solid propellant such as sodium azide mixed with an oxidizer such as potassium perchlorate, it has been proposed in U.S. Pat. No. 3,785,674 issued on Jan. 15, 1974 to Poole et al. to include a coolant chamber in the gas generator and to fill this chamber with a liquid halocarbon such as Freon.RTM. and to arrange for the halocarbon liquid to atomize in the nitrogen rich environment to reduce the temperature of the gas which is used to inflate the safety restraint (air bag). However, in this arrangement the gaseous combustion products are released directly into a chamber which contains the halocarbon liquid and which is closed by a burst disc. This of course, requires heating the liquid to its boiling point. The resulting mixture of gaseous freon and hot combustion products is reactive, and part of the freon decomposes. The decomposition of freon results in the formation of lower molecular weight halogen compounds (including HCl and HF), which are toxic. For this reason, freons are not used in hybrid air bag inflators.
U.S. Pat. No. 3,862,866 issued on Jan. 28, 1975 in the name of Timmerman et al. describes an arrangement which is essentially similar to the Poole et al. device, with the basic exception that water is used in place of halocarbon liquid. However, this arrangement is such that a slug of unvaporized liquid is apt to be shot out of the device only to result in the water being sprayed like a shower of rain throughout the interior of the air bag.
Thus, while these arrangements may find application as fire extinguishers of the nature disclosed in U.S. Pat. No. 5,449,041 issued on Sep. 12, 1995 in the name of Galbriath, wherein a solid propellant charge is ignited and used to drive a volume of liquid having flame suppressing capabilities, against a fire in a manner which suppresses and extinguishes it, they have failed to make the most efficient use of the cooling effect possible with the liquid used.
Another problem that these arrangements have failed to address is that of low temperature climates in which liquids, such as water, are apt to freeze and thus fail to achieve cooling of any degree, and/or even hinder the operation of the device by generating a block of solid material (ice) that is apt to either block the exits or turn into a missile which is fired out of the device in a highly undesirable manner.
The above problem is further aggravated in that the use of halocarbon liquids, which would tend to alleviate the freezing problem, are now severely restricted in light of various environmental considerations.